Electrically active implantable medical devices such as pacemakers, cardioverter/defibrillators, neurological stimulators and drug pumps are well known in the art. Such implantable medical devices are commonly powered by an internal power source, such as a battery, and are controlled by an internal controller, such as a microprocessor. The controller commonly controls additional circuitry to deliver appropriate therapy to the patient in whom the device has been implanted and to sense the patient condition using internal sensors. Further, the controller commonly controls a wireless communication system which enables the implantable medical device to exchange information and commands with medical devices external to the patient, as well as other implantable medical devices.
Such implantable medical devices are definitionally configured to be placed and physically isolated within the patient. As such, the physical size of the implantable medical devices may have a significant impact both on the places within the patient where the implantable medical device may be implanted and on patient comfort and quality of life. While a relatively large implantable medical device may have to be placed somewhat far from the site of therapy delivery owing to lack of space within the patient's anatomy close to the site of therapy delivery, a relatively smaller device may be placed either closer to or directly at the site of therapy delivery. In addition, while a relatively large implantable medical device may require large incisions and displacement of patient tissue during implantation, a relatively small implantable medical device may be implanted using small incisions with little tissue displacement. Moreover, while a relatively small device may substantially physically unobtrusive to the patient's lifestyle, and even, if very small, physically undetectable for the patient, a relatively large device may create highly visible bulges in the patient's skin and may have a meaningful impact on the patient's lifestyle.
Thus, it is broadly in the interest of both the patient and the medical professionals who work with the implantable medical devices that such devices are made as small as can be achieved while still meeting important requirements for therapy capabilities and longevity. To that end, efficiencies in the sizing of implantable medical devices have been sought through reductions in size of physical components, including electronic components, mechanical components such as leads and chemical components such as batteries. In addition, the physical layout of such implantable medical devices have been adjusted to more efficiently pack components in space.